Hot punching of metals



y 1956 J. SEJOURNET 2,756,494

HOT PUNCHING OF METALS Filed Oct. 10, 1952 T INVENIOR.

5 Jacques se ournef HIS ATTORNEYS United States Patent HOT PUNCi-IING on METALS Jacques Sejournet, Paris, France, assignor to Comptoir Industriel dEtirage et Profilage de Metaux, Paris, France, a corporation of France Application October 10, 1952, Serial No. 314,026

Claims priority, application France October 15, '1951 1 Claim. (Cl. 29424) This invention relates to hot piercing of metal billets or workpieces by a press acting upon a mandrel. It is particularly directed towards the preparation of blanks for hot extrusion of tubes.

Generally, in tube manufacture, billets with square cross sections are hot pierced in cylindrical containers. The cross section dimensions of these billets are such that during piercing the billets length remains substantially constant. Consequently, in the piercing operation displaced metal flows in a plane perpendicular to the piercing axis and fills free space between the container walls and the billet. Hence, operation stresses are relatively low.

Another method of hot piercing employs cylindrical billets having a diameter slightly smaller than that of the container in which they are pierced. In this operation displaced metal flows in two directions, one perpendicular to, and one parallel with the piercing axis. Like the above method, displaced metal first fills free space as described above; and next flows along the container Walls, therefore, stresses are relatively low.

In both operations the frictional stresses along the container walls are low and relatively unimportant. Hence, the container Walls and mandrel head on the piercing mandrel do not experience excessive wear and therefore have relatively good life. However, off-centered holes frequently appear in the pierced billet. Irregular flow of displaced metal during piercing, and failure to properly center the workpiece in the container account for some of the off-centered holes.

A third process first compresses a round, square or other shaped billet in a cylindrical container before piercing and thus eliminates any free space between the billet and the container. In this piercing operation the displaced metal fiows in a plane parallel with the piercing axis and against the container walls. This method produces well centered holes but creates a difficult problem in lubrication of the piercing mandrel head due to frictional stresses from the flow of displaced metal against the container walls and due to increased resistance to the piercing mandrel head which must both displace metal and overcome friction resistance to flow of metal against container walls. These factors have prevented industrial development of this process. Furthermore, this method is subject to rapid mandrel head and container wall wear, high maintenance cost of equipment and poor surface on the billet.

My invention provides an elficient method of hot piercing where surface of the billet and its bore are satisfactory, where the holes are well centered, and where the cost of repair and maintenance of equipment is substantially reduced, all of these advantages being simultaneously obtained. To accomplish this I first insert a heated workpiece into a cylindrical container. Next I place on the top surface of the workpiece, a substantial thickness of a glass-like lubricating material which is incombustible at piercing temperatures, has a melting range as contrasted with a true melting point and melts partially while "ice remaining viscous during piercing. Then I pierce the workpiece by forcing a mandrel and its mandrel head through the lubricating material and through the workpiece whereby the lubricating material under the influence of heat and pressure partially melts and continuously flows out around and over the mandrel head. My mandrel head has a cavity on its piercing face.

By glass-"Xe lubricating materials as used in this description and claim, I mean materials which are incombustible at piercing temperatures and which have a wide viscous range as contrasted with a true melting point. These materials have a wide range of temperatures over which they become increasingly less resistant to flow but remain viscous as contrasted with materials which have sharp melting points and hence, are subject to quickly becoming liquids or solids with changes in temperature. I have found glasses, slags and certain salts such as sodium borate, sodium metaphosphate and sodium silicates to be satisfactory and to possess the desired properties. One suitable slag which has a wide viscous range has the following analysis:

Percent SiOz 54 NazO 27 Sejournet, et al. Patent 2,538,917 describes more particularly, the glass-like lubricating materials which I require. These materials are to be distinguished from those which have been previously used and which do not produce satisfactory results. Such lubricants are oil, oil mixed with graphite, pitch and animal and vegetable fats.

In a modification of my process in addition to the above steps, I provide between the workpiece and the container, a layer of glass-like lubricating material, preferably glass cloth, around the workpiece. In this modification I either lubricate the walls of the container before inserting the heated workpiece or wrap a glass cloth around the workpiece and then insert it into the container. Other lubricants for use between the workpiece and the container walls which produce satisfactory results are salts such as barium chloride, sodium chloride and magnesium chloride, which salts have true melting points. In addition certain salts such as borax, sodium metaphosphates and sodium silicates which have a melting range instead of a true melting point are also satisfactory. I wish to point out that the lubricant between the workpiece and the container walls need not be of the same character as that placed upon the top of the workpiece prior to piercing.

Another modification of my process involves compressing the workpiece in the cylindrical container prior to the piercing step. In this compressing step I eliminate space between the workpiece and the container walls, thus insuring a well centered bore.

Some of the metals and alloys which can be satisfactorily pierced according to my invention are steel and steel and iron alloys, nickel and nickel-rich alloys, copper and copper-rich alloys, iron-free alloys, alloys low in iron which contain substantial amounts of one or more of the following alloying elements: nickel, cobalt, chromium, tungsten and molybdenum.

In the accompanying drawings I have shown certain preferred embodiments of my invention in which:

Figure 1 is a partial vertical section view through a container of a piercing press showing a mandrel and its mandrel head;

Figure 2 is a vertical section view of the mandrel head shown in Figure l;

Figure 3 is a vertical section view of a modification of a mandrel head;

Figure 4 is a partial vertical section view through the container of a piercing press showing flow of displaced metal as indicated by arrows in planes both perpendicular to and parallel with the piercing axis.

Referring to Figure 1, I first insert a steel workpiece 1, heated to piercing temperatures, preferably 1150 to 1200 G, into a cylindrical container 2, resting upon a base plate 3. Next I place a plate of glass 4 of substantial thickness upon the top surface of the workpiece. This glass plate has the properties of being incombustible at piercing temperatures, of having a melting range as contrasted with a true melting point, and of melting partially while remaining viscous during the piercing operation. Then I cut a disc from the glass plate by actuating a press (not shown) which forces a mandrel 5 and its mandrel head 6 through the glass plate to the top of the workpiece. As shown in Figures 1 and 2 the mandrel head 6 has a concave cavity 7 on its piercing face 8, and has a shank 9 for attaching it to the mandrel. Figure 3 shows a modification of a mandrel head 6' with a cavity 7' on its face 8'. Next I pierce the workpiece by forcing the mandrel and its head through to the base plate.

During piercing the cavity 7 in the mandrel head 8 holds the plate of glass 4 in contact with the heated workpiece and functions as a reservoir of lubricant throughout the operation.

This workpiece is heated to approximately 1200 C.

The container itself is in the neighbourhood of 300 C. from previous operations. Under these conditions a layer of the surface of the glass plate in contact with the workpiece melts and is viscous while the rest of the disc remains substantially solid. As the mandrel head moves forward the melted layer of glass flows out around and over the mandrel head. Then the next surface layer in contact with the workpiece melts and likewise flows out around and over the mandrel head. Thus, during the piercing operation there is a continuous flow of lubricant out around and over the mandrel head, which flow reduces the stresses encountered and increases mandrel head life.

The arrows 10 and 11 in Figure 4 show displaced metal flows. Arrow 10 illustrates flow in a direction perpendicular to the piercing axis. This occurs when there is a free space 12 between the workpiece and the container walls. The stresses in this sort of flow are not great. Arrow 11 shows metal flow in a plane parallel with the piercing axis. Such flow may occur when there is free space between the workpiece and the container walls in which case stresses are not great. However, when there is no free space between the workpiece and the container walls the displaced metal must flow in planes parallel with the piercing axis. In this case substantial stresses exist from the frictional resistance to the flow of metal along the container walls.

In one modification of my invention I interpose a lubricant between the workpiece and the container walls to reduce the frictional resistance to metal flow. I have found lubricants such as the glass-like lubricating materials described above satisfactory. These lubricants melt at least partially but remain viscous when subjected to the heat of the workpiece during piercing. As described above, I also use salts such as barium chloride, sodium chloride and magnesium chloride which have true melting points instead of a viscous range. These salts have the advantage of dissolving oxides which may be present on the surface of the workpiece and which would otherwise cause defects on the finished product. In using these lubricants I either lubricate the walls of the container before inserting the workpiece or wrap about the workpiece, sheets of the lubricant such as glass cloth or glass fibers before insertion in the container, or a combination of both lubricating the container walls and wrapping sheets of the lubricating materials about the workpiece.

In another modification of my invention I first compress the workpiece in the container by employing a mandrel having a head of substantially the same diameter as 7 tainer walls.

- piece.

With my invention I produce billets with well centered bores at appreciably less pressures than those used previously. With the reduced pressures I can reduce cost of production by increasing mandrel head and con tainer life and by lowering maintenance costs of equipment. In addition I lower processing costs arising from surface defects since billets pierced in accordance with my invention have improved surface qualities.

An example of the advantages afiorded by my invention is best shown by a comparison of three piercing operations. The first operation was performed with a hemispherical mandrel head with a lubricant of either graphite, coal or fine anthracite grains placed upon the top of the workpiece before piercing and with no lubricant between the workpiece and the container walls. The second operation was performed with the same type of mandrel and with a glass plate 3.5 mm. thick, placed upon the top of the workpiece before piercing and with the workpiece dipped in a bath of molten barium chloride to pro vide a lubricant between the container walls and the work- The third operation was performed according to my invention with a mandrel head of the type shown in Figure l, and in the same conditions of lubrication as in the second above mentioned operation. In the first operation after one extrusion the hemispherical mandrel head was unfit for further work because of heavy erosion on its surface. In the second operation the hemispherical mandrel had to be discarded after piercing 1 workpiece, the hemispherical mandrel having broken the glass plate and the lubrication by glass having thus been practically useless. In the third operation after piercing 20 workpieces the mandrel head was lightly cleaned with sandpaper and then used to pierce another 20 workpieces after which it remained perfectly serviceable.

Use of different shaped mandrel heads such as ogival, spherical-cap and hemispherical with the lubricants described above do not produce as satisfactory results since the lubricant tends to be driven back and to flow away from the mandrel head. This results in irregular and incomplete lubrication which in turn produces poor sorface on the billet.

While certain present preferred embodiments have been shown and described it will be understood that it may be otherwise embodied within the scope of the appended claim.

What I claim is:

In the piercing of a heated metal workpiece located in a chamber by forcing a mandrel head through the workpiece, the method of lubricating the mandrel head, which comprises placing on the top of said workpiece a thick layer of glass-like lubricating material, forcing the mandrel head through said layer of glass-like lubricating material to sever a disc of glass-like lubricating material from said layer, confining the severed disc of glass-like lubricating material within the piercing face of the mandrel head, and forcing the mandrel head through said workpiece the thickness of glass-like lubricating material and the rate of movement of the mandrel being such that the layer of said disc which is in contact with the workpiece, under the influence of heat and pressure is of such a thickness to melt and continuously flow out around and over said mandrel head throughout the piercing operation,

(References on following page) Refernces Cited in the file of this patent UNITED STATES PATENTS Ehrhardt Apr. 11, 1893 Hoopes Aug. 8, 1905 5 Knaebel Dec. 23, 1913 6 Batie Sept. 4, 1928 Simons Feb. 19, 1929 Sparks Nov. 4, 1941 Norton Jan. 1, 1946 Sherman Nov. 4, 1947 Sejournet et a1. Jan. 23, 1951 

1. IN THE PIERCING OF A HEATED METAL WORKPIECE LOCATED IN A CHAMBER BY FORCING A MANDREL HEAD THROUGH THE WORKPIECE, THE METHOD OF LUBRICATING THE MANDREL HEAD, WHICH COMPRISES PLACING ON THE TOP OF SAID WORKPIECE A THICK LAYER OF GLASS LIKE LUBRICATING MATERIAL, FORCING THE MANDREL HEAD THROUGH SAID LAYER OF GLASS-LIKE LUBRICATING MATERIAL TO SEVRE A DISC OF GLASS-LIKE LUBRICATING MATERIAL FROM SAID LAYER, CONFINING THE SEVERED DISC OF GLASS-LIKE LUBRICATING MATERIAL WITHIN THE PIERCING FACE OF THE MANDREL HEAD, AND FORCING THE MANDREL HEAD THROUGH SAID WORKPIECE THE THICKNESS OF GLASS-LIKE LUBRICATING MATERIAL AND THE RATE OF MOVEMENT OF THE MANDREL BEING SUCH THAT THE LAYER OF SAID DISC WHICH IS IN CONTACT WITH THE WORKPIECE, UNDER THE INFLUENCE OF HEAT AND PRESSURE IF OF SUCH THICKNESS TO MELT AND CONTINUOUSLY FLOW OUT AROUND AND OVER SAID MANDREL HEAD THROUGHOUT THE PIERCING OPERATION, LEAVING AT THE END OF THE PIERCING OPERATION A BODY OF GLASS-LIKE LUBRICATING MATERIAL WITHIN THE CONFINES OF THE PIERCING FACE OF SAID MANDREL HEAD. 